1. Field of the Invention
The present invention relates to a cooling control method, a cooling control apparatus, a cooling water amount calculation apparatus, a computer program, and a storage medium in a process of production of steel plate, more particularly relates to technology preferred for use for cooling steel plate immediately after rolling.
2. Description of the Related Art
Conventionally, cooling control designed to measure the temperature of the steel plate during cooled processing, change the amounts of cooling water sprayed on a top surface and a bottom surface of the steel plate so that a cooling end temperature becomes a desired temperature, and eliminating a difference between a top surface temperature and a bottom surface temperature of the steel plate so as to prevent shape deterioration of the steel plate occurring due to the difference between the top surface temperature and the bottom surface temperature of the steel plate has been proposed (see for example Japanese Patent Publication (B2) No. 7-41303).
Further, in the cooling method disclosed in Japanese Patent Publication (A) No. 60-210313, a top/bottom ratio of amounts of cooling water is determined by a coefficient determined from the size etc. of the cooled material. The steel plate temperature during cooling largely depends upon the amounts of cooling water and heat transfer coefficient. Namely, the heat transfer coefficient is a function of the surface temperature of the steel plate.
Accordingly, the state of the steel plate temperature at the time of the start of cooling, which differs for each cooling target, and the change of the heat transfer coefficient due to the change of the surface temperature of the steel plate during cooling, which changes with each instant, cannot be correctly reflected in the amounts of the cooling water. For this reason, deterioration of the shape of the steel plate could not be prevented with a high precision by just determining the top/bottom ratio of the amounts of water.
In order to solve the problem described before, the cooling method disclosed in Japanese Patent Publication (B2) No. 7-29139 predicts the temperature at the time of the cooling start based on the temperature at the time of the rolling end and calculates continuously changing surface temperature state and heat transfer coefficient by using a heat transfer formula using the predicted temperatures as the initial state so as to determine the water top/bottom ratio suppressing the deterioration of shape of the steel plate during cooling with a high precision.
However, as explained before, the heat transfer coefficient exerts a large influence upon the steel plate temperature at the time of the cooling start, therefore the cooling method disclosed in Japanese Patent Publication (B2) No. 7-29139 predicated on predicting the cooling start temperature at the time of the rolling end is susceptible to a variety of disturbances in the period from the rolling end to the cooling start. For this reason, the water top/bottom ratio determined at the time of the rolling end also includes a large amount of error, therefore the cooling method disclosed in Japanese Patent Publication (B2) No. 7-29139 had the problem that there was a limit to the suppression of shape deterioration of steel plate.
Therefore, as a technique for simultaneously solving the problems of the cooling methods disclosed in Japanese Patent Publication (A) No. 60-210313 and Japanese Patent Publication (B2) No. 7-29139, for example, in the cooling method disclosed in Japanese Patent Publication (A) No. 2-70018, the cooling top/bottom water rate ratio is calculated according to the temperatures measured at the cooling start position and the water top/bottom ratio giving a constant top/bottom temperature distribution is searched for and calculated by using a heat transfer formula considering the continuously changing surface temperature state and heat transfer coefficient.
In the case of the cooling method disclosed in Japanese Patent Publication (A) No. 2-70018 explained before, it is believed that the water top/bottom ratio can be found with a high precision. However, in the case of this cooling method, the heat transfer formula is used for repeated calculation to search for the top/bottom ratio of the amounts of cooling water, therefore the amount of calculation becomes huge. For this reason, there was the problem that tremendous time was needed until obtaining the results of calculation. As a result, there is a great possibility of the occurrence of the trouble of a delayed start of spraying of water after the steel plate enters the cooling apparatus, the trouble of the steel plate having to be stopped and kept on standby before the cooling apparatus until the water starts to be sprayed, etc., therefore the implementation was difficult.